Laminated glass is a type of safety glass that holds together when shattered. In the event of breaking, it is held in place by an interlayer, typically of polyvinyl butyral (PVB), polyurethane (PU) or ethylene-vinyl acetate (EVA), between its two or more layers of glass. The interlayer keeps the layers of glass bonded even when broken, and its high strength prevents the glass from breaking up into large sharp pieces. This produces a characteristic “spider web” cracking pattern when the impact is not enough to completely pierce the glass. In the case of thermoset EVA, a cross-linked EVA bonding with the glass is achieved. All of the above interlayers can be used with non-glass substrates, such as polycarbonate, polyacrylic, PET or other types of plastics, to achieve a similar bonding benefit.
Laminated glass is normally used when there is a possibility of human impact or where the glass could fall if shattered and also for architectural applications. Skylight glazing and automobile windshields typically use laminated glass. In geographical areas requiring hurricane-resistant construction, laminated glass is often used in exterior storefronts, curtain walls and windows.
Laminated glass is also used to increase the sound insulation rating of a window, where it significantly improves sound attenuation compared to non-laminated glass panes of the same thickness. For this purpose a special “acoustic PVB” compound is used for the interlayer. In the case of EVA material, no additional acoustic material is required, since EVA provides sound insulation. An additional property of laminated glass for windows is that PVB and EVA interlayer can comprise an ultraviolet (UV) absorber that can block most ultraviolet radiation. For example, a thermoset EVA could block up to 99.9% of the UV rays.
Laminated glazings often have inserts that are laminated between the glass or plastic substrates and clear interlayers to create a decorative or functional laminated glazing. Examples of decorative inserts can be colored plastics, fabric or pictures on paper or silk. Functional inserts include smart technologies such as SPD, as well as LC, photochromic, electrochromic and thermochromic materials.
Light valves have been known for more than eighty years for use in the modulation of light. Such light valves have been utilized in numerous applications during that time including but not limited to, e.g., alphanumeric displays and television displays; filters for lamps, cameras, displays and optical fibers; and windows, sunroofs, toys, sun visors, eyeglasses, goggles, mirrors, rearview mirrors, light pipes and the like to control the amount of light passing therethrough or reflected therefrom as the case may be. Examples of windows include, without limitation, architectural windows for commercial buildings, greenhouses and residences, windows, visors and sunroofs for automotive vehicles, boats, trains, planes and spacecraft, windows for doors including peepholes, and windows for appliances such as ovens and refrigerators including compartments thereof.
As used herein, the term “light valve” describes a cell formed of two walls that are spaced apart by a small distance, with at least one wall being transparent. The walls have electrodes thereon, usually in the form of transparent, electrically conductive coatings. Optionally the electrodes on the walls may have thin transparent dielectric overcoatings thereon. The cell contains a light-modulating element (sometimes herein referred to as an activatable material) which may, without limitation, be either a liquid suspension of particles or alternately, all or a portion of the entire element may comprise a plastic film in which droplets of a liquid suspension of particles are distributed.
The liquid suspension (sometimes herein referred to as a light valve suspension or as a liquid light valve suspension) comprises small particles suspended in a liquid suspending medium. In the absence of an applied electrical field, the particles in the liquid suspension of a SPD light valve may assume random positions due to Brownian movement. Hence, a beam of light passing into the cell is reflected, transmitted or absorbed depending upon the cell structure, the nature and concentration of the particles and the energy content of the light. The SPD light valve using this type of particle movement is thus relatively dark in the OFF state. However, when an electric field is applied through the liquid light valve suspension in the light valve, the particles become aligned and for many suspensions most of the light can pass through the cell. The SPD light valve is thus relatively transparent in the ON state.
For many applications it is preferable for all or part of the activatable material, i.e., the light modulating element, to be a plastic film rather than a liquid suspension. For example, in a light valve used as a variable light transmission window, a plastic film in which droplets of liquid suspension are distributed is preferable to a liquid suspension alone because hydrostatic pressure effects, e.g., bulging associated with a high column of light suspension, can be avoided through use of a film and the risk of possible leakage can also be avoided. Another advantage of using a plastic film is that, in a plastic film, the particles are generally present only within very small droplets and, hence, do not noticeably agglomerate when the film is repeatedly activated with a voltage.
A light valve film (also sometimes herein referred to as an SPD film) as used herein means a film or sheet, or more than one thereof, comprising a suspension of particles used or intended for use in a light valve. Such light valve film usually comprises a discontinuous non-crosslinked phase of liquid comprising dispersed particles, termed a liquid light valve suspension, such discontinuous phase being dispersed throughout a curable continuous phase enclosed within one or more rigid or flexible solid films or sheets. Cured emulsion, which may form part of a light valve film, is sometimes also referred to as a film or film layer. The light valve film and/or a laminated glass stack comprising the light valve film may also comprise one or more additional layers such as, without limitation, a film, coating or sheet or combination thereof, which may provide the light valve film with one or more of, for example, (1) scratch resistance, (2) protection from ultraviolet radiation, (3) reflection of infrared energy, (4) electrical conductivity for transmitting an applied electric or magnetic field to the activatable material, (5) dielectric overcoatings, (6) color tinting, (7) heating elements and/or (8) acoustic control. The additional layers may be adhered to said light valve film with a pressure sensitive adhesive (PSA) known to those skilled in the art or with additional plies of interlayer during the lamination procedure as discussed below in the Summary of the Invention.
A common (but non-limiting) construction for an SPD film comprises five layers, namely, in order from a first side to a second, opposed side: (1) a first sheet of polyethylene terephthalate (“PET”) plastic, conveniently 5-7 mils in thickness, (2) a very thin transparent, electrically conductive coating of indium tin oxide (“ITO”) or alternative conductive coating, acting or capable of acting as an electrode, on the first sheet of PET, (3) a layer of cured (i.e., cross-linked) SPD emulsion, usually 2-5 mils in thickness and, (4) a second ITO coating (or an alternative conductive coating) acting or capable of acting as an electrode on (5) a second PET plastic substrate. As stated previously, additional layers which provide other functions may optionally be added to the five-layer SPD film described above. Typically, copper foil, conductive fabric or the like are affixed to the electrodes so that they extend beyond the perimeter of the SPD film for convenient busbar connection to a suitable voltage source. Furthermore the SPD film can be laminated, for example, with transparent hot melt adhesive films and/or glass or thicker transparent plastic sheets to provide strength and rigidity and to protect various parts of the combined unit from environmental conditions which may, otherwise, damage its performance characteristics.
U.S. Pat. No. 5,409,734 exemplifies a type of non-crosslinked light valve film that is made by phase separation from a homogeneous solution. Light valve films made by cross-linking (curing) of emulsions are also known. The methods of the present invention are specifically directed to the use of the latter type of film, i.e., film comprising a layer formed by cross-linking an emulsion, and to laminated films produced therewith. See, for example, U.S. Pat. Nos. 5,463,491 and 5,463,492, and U.S. Pat. No. 7,361,252, all of which are assigned to the assignee of the present invention. Various types of SPD emulsions, and methods of curing the same, are described in U.S. Pat. Nos. 6,301,040, 6,416,827, and 6,900,923 B2, all of which are assigned to the assignee of the present invention. A non-limiting example of such a film from Example 5 of U.S. Pat. No. 6,900,923 B2 is produced as follows: 0.002 g of Irgacure 819 (Ciba Specialty Chemicals) photoinitiator (“PI”) was dissolved in 2 mL of chloroform and added to 1 g of the matrix polymer described in Example 1. The PI solution was thoroughly mixed with the matrix polymer and the chloroform solvent was removed by placing the mixture inside of a vacuum oven for 30 minutes at 60° C. To this was added 0.62 g of polyiodide crystal paste containing the lauryl methacrylate/HEMA suspending polymer (0.56 g, as synthesized in example 3 of the patent). The resulting mixture was thoroughly mixed and the emulsion obtained was applied onto a conductive coated polyester substrate as a 2 mil thick coating using a doctor blade, mated with a blank conductive coated polyester substrate and cured with ultraviolet radiation (8600 mJ/cm2/min) for 2 min and 30 seconds. Such films and variations thereof may be cured through cross-linking brought about by exposing the films to (1) ultraviolet radiation, (2) electron beams or (3) heat.
All of the patents and patent applications and other references cited in this application are incorporated herein by reference.